1. Field of the Invention
The present invention relates to hollow metal objects possessing a space in the core portion enabling the of passing fluids such as liquids and gasses through the space.
2. Description of the Background Art
Hollow metal objects have to date been utilized as piping or tubing, as conduits for passing fluids such as gasses and liquids, and further, as components for forming the framework of structures. Owing to metals' abundant ductility, their capacity for being worked plastically, and the suitable rigidity they posses, they are useful in fields that demand complex shapes to which resins and sintered materials cannot be adapted. The electro-conductivity that metals posses, furthermore, enables using them as part of electrical circuitry. Likewise, because these properties may be freely selected according to type of metal, processing level, heat treatment, etc., their industrial fields of use have grown extremely wide-ranging.
Especially with hollow metal objects, small-diameter tubing whose outer diameter is several mm or less is finding practical applications, apart from use as ordinary fluid passages, in specialized applications such as electrodes in electro-discharge machining of fine holes, and in medical instruments. Owing to demands that mechanical strength be secured to a certain extent, it is desirable to utilize tungsten or molybdenum—which are high-melting-point metals—or stainless steel, as raw materials in these applications.
With their plastic deformation ability being generally low at room temperature, high-melting-point metals are materials that are difficult to work, and are therefore not readily fabricated into hollow forms, compared with other, soft metals. A method that, by working metal filaments into twisted wire and brazing—by filling with a brazing filler—the gaps between companion filaments, provides a hollow metal object for electro-discharge machining is disclosed in Japanese Pub. Pat. App. 2001-157925 as a technique for fabricating a hollow form from a high-melting-point metal.
Pipe-drawing, spiraling, and seaming techniques are generally employed as methods of fabricating hollow metal objects. These methods are flourishingly used as means for manufacturing hollow forms of comparatively large diameter from metals rich in ductility, but are extremely difficult to apply to situations, which are the target of the present invention, in which small-diameter tubing of 1 mm or less maximum diameter is manufactured, and in which low-plastic-workability, high-melting-point metals are the raw material. Because this requires imparting considerable plastic deformation to the material serving as the raw material in manufacturing small-diameter hollow forms, securing the dimensional precision and formational precision of the finished product has been exceedingly problematic, even given that processing by repeatedly implementing deformation and annealing steps has been possible.
To counter these difficulties, with the hollow metal object disclosed in Japanese Pub. Pat. App. 2001-157925 first-metal filaments that will constitute the metal hollow form are twisted together around second-metal filaments that serve as a brazing material, and by thereafter heating to or above the melting point of the filaments of the second metal that serve as a brazing material, the filaments of the first metal are brazed, yielding a manufactured hollow metal object. Although manufacturing thin hollow metal objects whose maximum diameter is 0.04 mm to 0.5 mm has been possible with this method, the thickness of the brazing filler inside the hollow form turns out to be unstable; moreover, protrusions due to interfering matter and bubbles have been prone to arise, which in practice have proven to be a cause of blockage in passing fluids.